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ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it

With new binutils, gcc may get smart with its optimization and change a jmp
from a 5 byte jump to a 2 byte one even though it was jumping to a global
function. But that global function existed within a 2 byte radius, and gcc
was able to optimize it. Unfortunately, that jump was also being modified
when function graph tracing begins. Since ftrace expected that jump to be 5
bytes, but it was only two, it overwrote code after the jump, causing a
crash.

This was fixed for x86_64 with commit 8329e818f1, with the same subject as
this commit, but nothing was done for x86_32.

Cc: stable@vger.kernel.org
Fixes: d61f82d066 ("ftrace: use dynamic patching for updating mcount calls")
Reported-by: Colin Ian King <colin.king@canonical.com>
Tested-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt (Red Hat) 2016-12-08 12:48:26 -05:00 committed by Steven Rostedt
parent 9c1f6bb8c8
commit 847fa1a6d3

View File

@ -889,8 +889,8 @@ ftrace_graph_call:
jmp ftrace_stub
#endif
.globl ftrace_stub
ftrace_stub:
/* This is weak to keep gas from relaxing the jumps */
WEAK(ftrace_stub)
ret
END(ftrace_caller)